This invention relates to apparatus for use in the manufacture of filter means, more particularly tobacco smoke filter elements. More specifically, the instant inventive concepts are primarily concerned with the manufacture of filter means for cigarettes, although the apparatus of this invention is generally useful in the manufacture of other filter means, particularly for tobacco smoking means, whether they be cigarettes, cigars, pipes or the like. Since filters for cigarettes are particularly commercially important, the basic embodiments of the instant invention will be discussed as they relate to the production of filtered cigarettes.
In making tobacco smoke filters for use in connection with cigarettes and the like, bondable continuous filamentary tows of substantially continuous thermoplastic fibers, such as plasticized cellulose acetate fibers, polyethylene fibers, polypropylene fibers nylon fibers and the like, have conventionally been employed as the starting material. The term "continuous filamentary tow", as used in this specification and the appending claims, is intended to define a material such as that which results when filaments extruded from a plurality of spinnerets are brought together and combined to form a continuous body of fibers randomly oriented primarily in a longitudinal direction. In such a tow, the filaments are generally longitudinally aligned in substantially parallel orientation, but include crimped portions which may form short sections running more or less at random in non-parallel diverging and converging directions. Although the apparatus of this invention is applicable to the various filamentary materials of this type, since plasticized cellulose acetate is the most common thermoplastic fiber used in the manufacture of cigarette filters, the specification hereof will be generally set forth in terms of this material. However, it is to be understood that the instant inventive concepts are not to be limited to this preferred embodiment.
In the manufacture of filters for cigarettes and the like, a number of different factors must be considered. Filtration efficiency, which is the capacity to remove unwanted constituents from smoke, while highly desirable is only one factor important in producing a commercially acceptable filter. Other factors, such as pressure drop, taste, hardness and cost also determine commercial acceptance of these products. For example, cellulose acetate, one of the most commonly used substances in manufacturing cigarette filters has a relatively low filtration efficiency. Increased filtration efficiency obtained by increasing the density or length of a cellulose acetate fiber may cause a pressure drop across the filter which is excessive and commercially unacceptable. The use of activated carbon or other such materials having higher filtration efficiency may increase cost and deleteriously affect taste.
In recent years, air dilution has become a popular technique for compensation for the relatively low filtration efficiency of cigarette filters which have a pressure drop sufficiently low for commercial acceptance. In this technique, ventilating air is drawn into the filter peripherally and dilutes the smoke stream from the tobacco to thereby reduce the quantity of tar and other unwanted tobacco constituents drawn into the smoker's mouth with each puff.
The air dilution technique provides several obvious advantages:
It is an extremely economical method for reducing various solid phase constituents of tobacco smoke, generally referred to as "tar".
It also enables the removal or reduction of certain gas phase constituents of tobacco smoke such as carbon monoxide and nitrous oxide.
By varying the quantity of air introduced into the filter with each puff, it permits control, within reason, of the filtration process in order that efficiency and taste can be balanced.
One of the major challenges to the cigarette filter industry has been to design a filter and filter production techniques and apparatus for producing, at high speeds, large numbers of low cost filters capable of utilizing the air dilution technique. When the air dilution technique first became commercially important, most cigarette filters were produced with an over-wrap material applied to the outside of the filament bundle comprising the filter element in order to achieve a dimensionally stable product. The manufacturing process produced an axially elongated rod comprising a core of filaments contained by a surrounding over-wrap material called the "plug-wrap". After cutting the filter rods into small segments or plugs suitable for use as cigarette filters, a tipping over-wrap secured the segments to a tobacco column comprising a core of tobacco surrounded by a cigarette paper over-wrap. With the air dilution technique, cigarette filters produced in the foregoing mannner required a porous or permeable plug-wrap in order that the air introduced generally through selectively provided perforations in the tipping over-wrap merged with and diluted the smoke coming from the tobacco column.
Because the use of plug wrap has certain disadvantages in general discussed in some detail in U.S. Pat. Nos. 3,313,306 and 3,377,220 granted Apr. 11, 1967 and Apr. 9, 1968, respectively, the subject matter of which are incorporated herein in their entirety by reference, techniques for producing non-wrapped dimensionally stable filter elements were developed. The significance of producing a non-wrapped, dimensionally stable filter rod is even more pronounced for use in air diluted cigarettes in view of the high cost of porous plug-wrap materials.
Numerous techniques are available for producing both plug-wrapped and non-wrapped filter elements from the continuous filamentray tow. In the case of non-wrapped filter elements, for example, such techniques may involve either a mechanical or pneumatic conveyance of the tow through various processing stations, and generally all of the known techniques involve heat bonding of the filamentary tow materials to form a dimensionally stable filter rod. This may, for example, be effected by the peripheral injection of steam into the filamentary tow as the tow is conveyed axially through a tubular heating station. In all cases, it is then necessary to stabilize and harden the rod for further processing by cooling the heated tow. When steam is used for heat bonding, it may also be preferable, in addition to cooling the rod, also to remove excess moisture. In low-speed processes or in processes where adequate space is available, the design of apparatus used for cooling the rod, for example by the injection of coolant gas, may not be particularly critical. In high speed production, however, where the rod is travelling at speeds in excess of 400 meters per minute, or in processes where space is a factor, it is desirable to have an extremely effective rod cooling apparatus capable of providing rapid cooling of the rod in a minimum length of travel. Moreover, prior to cooling, the filter rod is somewhat fragile, and accordingly the cooling apparatus should, desirably, be capable of maintaining the rod shape without damage to the rod surface. It is an object of the present invention to provide a cooling apparatus suitable for this purpose.